Pulp suspensions are widely used for making cellulosic products such as, for example, pulp and paper, and contain, apart from cellulosic fibres, also compounds which have a negative impact on the production process. Such compounds are found both in cellulosic suspensions originating from virgin pulp and from recycled pulp.
In virgin pulp suspensions such disturbing/detrimental substances are primarily hemicellulose, lignin as well as lipophilic and hydrophilic extractives. Apart from the cellulose, these substances are to a varying extent dissolved or colloidally dispersed into the process waters during the pulping and bleaching operations. Compounds which are released during pulping and bleaching operations are commonly referred to as pitch. Examples of pitch include wood resins such as lipophilic extractives (fatty and resin acids, sterols, stearyl esters, triglycerides), and also fats, terpenes, terpeniods, waxes, etc.
In recycled pulp suspensions the compounds having a negative influence on the paper making process mainly consist of glues, hot-melt plastics inks and latex, just to mention a few compounds—which are commonly referred to as stickies. Apart from pitch and stickies the suspension also contains charged contaminants like salts and various wood polymers of which the charged, low charged or non-charged compounds compete with the cellulose with respect to the adsorption and interaction with added performance chemicals such as drainage and retention aids, sizing agents, etc. Usually such disturbing compounds are referred to as anionic trash.
All of the above-mentioned compounds interfere with the pulp and paper making processes in various ways. For instance, some of them precipitate due to changes in the properties of the pulp suspension and are eventually deposited on various mechanical parts of the paper machine such as, for example, screens and felts. Over time, the deposits will lead to breakdowns on the paper machine often in form of breaking of the paper web, whereby the paper machine has to be stopped for cleaning. Furthermore, paper mills tend to re-circulate the white water to a greater extent than previously, which increases the presence of disturbing and detrimental substances in the suspension.
Various additives have been used in order to decrease the negative impact of the above-mentioned detrimental/disturbing substances. For example, talc has been widely used for adsorbing pitch and stickies. Also various types of clays have been employed for reducing the impact of detrimental compounds.
Japanese laid-open patent application No. 1985-94687 relates to a pitch-adsorbing agent containing hydrotalcite.